LOUISVILLE, Ky. — When Alison Lundergan Grimes, Kentucky’s Democratic Senate candidate, welcomed former President Bill Clinton to a fund-raiser here Tuesday, she offered a rendering of recent political history suited for red-state Democrats: Mr. Clinton’s tenure was showered with praise, former President George W. Bush was mildly scorned, and President Obama was implicitly rebuked.

“We all know what the problem is: it’s a Washington, D.C., that just doesn’t understand Kentucky,” Ms. Grimes said.

Her gibes at the capital’s “dysfunction” were chiefly aimed at her likely opponent, Mitch McConnell, the Senate Republican leader, but her nostalgia for the 1990s, when Ms. Grimes was in her teens, and her lament about the present was also aimed at linking herself to Mr. Clinton and distancing herself from Mr. Obama.

The former president’s presence on the stage also underscored a larger truth of the 2014 midterm campaign: Mr. Clinton is embraced in states, mainly in the South and the West, where Mr. Obama is all but unwelcome.

So the party is again turning to Mr. Clinton to help Democrats in seven of the most competitive Senate races, all of which are in states Mr. Obama lost in 2012. “He’s probably the most popular national Democrat alive,” Gov. Steve Beshear of Kentucky, a fellow Democrat, said of the former president.

Democratic strategists, and some candidates, are nearly giddy in discussing Mr. Clinton’s approval ratings in private polling but are far more sober when asked about Mr. Obama. “I’m a Clinton Democrat through and through,” said Ms. Grimes, Kentucky’s secretary of state, in an interview, suggesting that it was highly unlikely she would invite Mr. Obama to Kentucky.

Mr. Clinton is familiar with Mr. Obama’s standing in the sixth year of his presidency; Mr. Clinton was not a coveted surrogate either at a similar point in his second term. And Mr. Obama’s aides say that the lack of desire for him is rooted more in structural politics than a matter of his declining popularity.

“In some of these states, it wouldn’t make sense for a sitting Democratic president to come in at the height of their popularity,” said Dan Pfeiffer, a senior adviser to Mr. Obama. Kentucky may be one of those, as it represents one of the few states where Democrats believe they can pick up a seat.

Mr. Pfeiffer said Mr. Obama was not likely to appear at campaign rallies for Democratic candidates until after Labor Day and acknowledged that he might never show up for some of the key Senate races. But he said that even if the president never set foot in a state like Kentucky, or any of the other red states with competitive races, Mr. Obama would aid Democratic candidates there by urging his supporters to register to vote and turn out, and by raising money.

“There are ways in which we can help using the president’s grass-roots network or through targeted appeals,” Mr. Pfeiffer said, noting that Mr. Obama’s extensive list includes supporters even in states that are overwhelmingly Republican. “The challenge this year is to get Democrats to come out to the polls, and the president has a unique ability to do that.”

So when it comes to taking to the stump this year, much of the work will fall to Mr. Clinton, who plainly relishes the task.

“Getting Bill Clinton on the campaign trail is like force-feeding sugar to an ant,” said Mr. Clinton’s former adviser Paul Begala. “You don’t have to ask him twice.”

Photo

The shadow of former President Bill Clinton as he applauded Alison Lundergan Grimes, a Senate candidate in Kentucky.Credit
Luke Sharrett/Getty Images

As the former president made his national midterm campaign debut to loud applause in a state he had carried twice, he smiled broadly and made sure the cameras caught him and Ms. Grimes at angles made for future advertisements. “I love Kentucky,” Mr. Clinton drawled soon after taking to the lectern Tuesday, claiming to cheer for both the University of Kentucky and University of Louisville basketball teams.

He was on safe terrain venerating the locally beloved basketball programs. But he entered riskier territory when he repeatedly praised Mr. Beshear’s statewide rollout of the new health law and sought to defend Democrats generally on an issue Ms. Grimes was not highlighting in her campaign because of its unpopularity. Should former Secretary of State Hillary Rodham Clinton run for president in 2016, however, it is important that the measure be seen as more of an unalloyed success than it is today.

“Albert Einstein could have written that bill in a closet, and there would have been problems with it,” Mr. Clinton said.

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The peril posed by what conservatives call Obamacare underscores the limitations of just what Mr. Clinton, popular as he may now be, can do for Democratic candidates running in conservative-leaning states this year.

Kentucky, for example, is a national model for the law; 244,000 residents of the state now have health care because of the Affordable Care Act. Just in the last month, Mr. Beshear was a guest in the first lady’s box at Mr. Obama’s State of the Union address and at a White House state dinner, both invitations widely seen as a way of thanking the governor.

Yet despite what Democrats see as the success of the law here, it is Republicans who are focused on the topic. A “super PAC” supporting Mr. McConnell has attacked Ms. Grimes on the issue.

“You’ve got a president that is not very popular in Kentucky,” Mr. Beshear said, all but shrugging when asked to reconcile the apparent political danger of a law expanding health insurance in a poor state. “In politics, you try to walk that fine line.”

Ms. Grimes sought to do just that in the interview. She praised the enactment of the health measure in Kentucky, saying that the state was “leading the nation” in carrying it out.

But she was quick to work in a not-so-subtle dig at Mr. Obama.

“When Washington politicians make promises that ‘if you like your plan and your doctor, you can keep it,’ we actually live up to it,” she said.

In a race that is considered close and bound to grow highly negative, Mr. Clinton cited Mr. McConnell’s penchant for playing a tough brand of politics that had helped him win five terms and said Ms. Grimes could not compete with him on that plane.

“You got to beat him with this,” Mr. Clinton said near the end of his remarks, holding up a pamphlet with Ms. Grimes’s policy proposals.

Ideally for Ms. Grimes, he would have ended there. But then the former president referred again to Mr. Beshear’s efforts with the health law as part of an effort “to make health care work for more people.”

“That’s a very good thing,” Mr. Clinton said.

A version of this article appears in print on February 26, 2014, on Page A16 of the New York edition with the headline: Ex-President Ventures Where Some Might Not. Order Reprints|Today's Paper|Subscribe